In this study we aim to define the physiological correlates and consequences of shiftwork in a hospital nursing staff. The subjects consist of 15 permanent nightshift workers and 15 rotators to nightshift. Major data collection techniques include: polygraphic recordings of sleep, 20 minute plasma samples for hormone concentration curves, body temperature measurements, and questionnaires concerning prior and ongoing sleep-wake behavior, well being, and performance. The emphasis is therefore on detailed study of a variety of concomitant rhythmic functions in individual shiftworkers. We hypothesize that temporal misalignments of the phases of these functions ("desynchronization") are related to the development of symptoms and performance decrements, particularly in the rotators. We are also interested in the individuality of physiological response to altered work schedules. Can categories of physiological response, and therefore of shiftworkers, be defined? If so, can simple predictors be developed to preselect those individuals who are physiologically best suited for shiftwork?